The tethered Moon

Zahnle, Kevin; Lupu, Roxana; Dobrovolskis, Anthony R.; Sleep, Norman H.

doi:10.1016/j.epsl.2015.06.058

Cited by 58 publications

(99 citation statements)

References 48 publications

(104 reference statements)

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“…The uppermost few hundred meters to few kilometers were solid; lava episodically erupted to the surface and froze. The nascent Earth contained only enough heat to drive this internally heated runaway greenhouse for *10 My (Zahnle et al, 2015). Afterward, the climate transitioned to a solar-heated greenhouse with *200°C surface temperatures at 100 bar CO 2 .…”

Section: Geological Time Constraintsmentioning

confidence: 99%

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Geological and Geochemical Constraints on the Origin and Evolution of Life

Sleep

2018

Astrobiology

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The traditional tree of life from molecular biology with last universal common ancestor (LUCA) branching into bacteria and archaea (though fuzzy) is likely formally valid enough to be a basis for discussion of geological processes on the early Earth. Biologists infer likely properties of nodal organisms within the tree and, hence, the environment they inhabited. Geologists both vet tenuous trees and putative origin of life scenarios for geological and ecological reasonability and conversely infer geological information from trees. The latter approach is valuable as geologists have only weakly constrained the time when the Earth became habitable and the later time when life actually existed to the long interval between ∼4.5 and ∼3.85 Ga where no intact surface rocks are known. With regard to vetting, origin and early evolution hypotheses from molecular biology have recently centered on serpentinite settings in marine and alternatively land settings that are exposed to ultraviolet sunlight. The existence of these niches on the Hadean Earth is virtually certain. With regard to inferring geological environment from genomics, nodes on the tree of life can arise from true bottlenecks implied by the marine serpentinite origin scenario and by asteroid impact. Innovation of a very useful trait through a threshold allows the successful organism to quickly become very abundant and later root a large clade. The origin of life itself, that is, the initial Darwinian ancestor, the bacterial and archaeal roots as free-living cellular organisms that independently escaped hydrothermal chimneys above marine serpentinite or alternatively from shallow pore-water environments on land, the Selabacteria root with anoxygenic photosynthesis, and the Terrabacteria root colonizing land are attractive examples that predate the geological record. Conversely, geological reasoning presents likely events for appraisal by biologists. Asteroid impacts may have produced bottlenecks by decimating life. Thermophile roots of bacteria and archaea as well as a thermophile LUCA are attractive.

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Section: Geological Time Constraintsmentioning

confidence: 99%

“…1). The present Earth formed after the Moonforming impact at *4.5 Ga (Zahnle et al, , 2015Sleep et al, 2014). The mantle froze, and the surface became solid over a period of several million years.…”

Section: Geological Time Constraintsmentioning

confidence: 99%

Geological and Geochemical Constraints on the Origin and Evolution of Life

Sleep

2018

Astrobiology

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“…Accordingly, we stochastically remove bodies from the population in our three-body simulations such that the average loss as long the duration of the lunar magma ocean crystallization is sufficiently short, such a solution is viable and, indeed, necessary in a tidal evolution scenario recently described 30 .…”

Section: Methodsmentioning

confidence: 99%

Collisionless encounters and the origin of the lunar inclination

Pahlevan

Morbidelli

2015

Nature

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The Moon-forming impact is thought to have generated a compact circumplanetary disk (within < 10 Earth radii) from which the Moon rapidly accreted. Like Saturn's rings, the proto-lunar disk is expected to become equatorial on a timescale rapid relative to its evolutionary timescale. Hence, so long as the proto-lunar material disaggregated into a disk following the giant impact, the Moon is expected to have accreted within ~1° of the Earth's equator plane 6 . Tidal evolution calculations suggest that for every degree of inclination of the lunar orbit plane relative to the Earth's equator plane at an Earth-Moon (EM) separation of 10 Earth radii (R E ), the current lunar orbit would exhibit ~1/2° of inclination relative to Earth's orbital plane [7][8][9] . The modern ~5° lunar inclination wouldwithout external influences -translate to a ~10° inclination to Earth's equator plane at 10 R E shortly after lunar accretion. This ~10x difference between theoretical expectations of lunar accretion and the EM system has become known as the lunar inclination problem.Previous work on this problem has sought to identify mechanisms such as a gravitational resonance between the newly formed Moon and the Sun 12 or the remnant proto-lunar disk 13 that can excite the lunar inclination to a level consistent with its current value.Neither of these scenarios is satisfactory, however, as the former requires particular values of the tidal dissipation parameters while the latter has only been shown to be viable in an idealized system where a single, fully-formed Moon interacts with a single pair of resonances in the proto-lunar disk. Moreover, prior works have all assumed that the excitation of the lunar orbit was determined during interactions essentially coinciding with lunar origin. Here, we propose that the lunar inclination arose much later as a consequence of the sweep-up of remnant planetesimals in the inner Solar System. After the giant impact and at most ~10 3 years 14,15 , the Moon has accreted, interacted with 13 and caused the collapse of the remnant proto-lunar disk onto the Earth 6 , passed the evection resonance with the Sun 3,12,16 , and begun a steady outward tidal evolution. On a timescale (~10 6 -10 7 years) rapid relative to that characterizing depletion of planetesimals in the final post-Moon formation stage of planetary accretion 17 (called "late accretion"), the lunar orbit expands through the action of tides to an EM separation of ~20-40 R E . In this time, the lunar orbit transitions from precession around the spin-axis of Earth to precession around the heliocentric orbit normal vector 8 , and its inclination becomes insensitive to the shifting of the Earth's equatorial plane via subsequent accretion 18 .However, as we show below, lunar inclination becomes more sensitive to gravitational interactions with passing planetesimals as the tidal evolution of the system proceeds. The sensitivity is such as to render the lunar orbital excitation a natural outcome of the sweepup of the leftovers of accretion and to yield ...

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“…This observation rules out simple models where all the bombardment occurred soon after the moon‐forming impact or all within a terminal event at ∼3.9 Ga. Studies of the morphology of old lunar basins indicate that they formed soon (within 50 Myr) after the crystallization of the magma ocean while the upper mantle was still hot [ Kamata et al ., ]. The Earth took ∼2–10 Myr after the moon‐forming impact to cool enough that oceans could condense, as a thick water‐vapor and CO 2 atmosphere blanketed the planet [e.g., Abe and Matsui , ; Sleep et al ., ; Zahnle et al ., ]. The surface did not become habitable until most of the CO 2 entered the mantle by a process with the net effect of subduction.…”

Section: Modeling Approaches With Regard To Veneer Componentmentioning

confidence: 99%

“…The abundant species, H 2 O, FeO, CO 2 , CH 4 , and H 2 , in the silicate liquid controlled redox [ Li et al ., ]. The atmosphere in equilibrium with the mantle, which circulated continually through the surface boundary layer [ Sleep et al ., ; Zahnle et al ., ], was thus also near a Fe‐FeO buffer. However, the precise H 2 O/H 2 ratio in the gas is poorly constrained [e.g., Hirschmann , ].…”

Section: Iron Mass Balances For the Moon And Earthmentioning

confidence: 99%

Asteroid bombardment and the core of Theia as possible sources for the Earth's late veneer component

Sleep

2016

Geochem Geophys Geosyst

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The silicate Earth contains Pt-group elements in roughly chondritic relative ratios, but with absolute concentrations <1% chondrite. This veneer implies addition of chondritelike material with 0.3-0.7% mass of the Earth's mantle or an equivalent planet-wide thickness of 5-20 km. The veneer thickness, 200-300 m, within the lunar crust and mantle is much less. One hypothesis is that the terrestrial veneer arrived after the moon-forming impact within a few large asteroids that happened to miss the smaller Moon.Alternatively, most of terrestrial veneer came from the core of the moon-forming impactor, Theia. The Moon then likely contains iron from Theia's core. Mass balances lend plausibility. The lunar core mass is ~1.6×10 21 kg and the excess FeO component in the lunar mantle is 1.3-3.5×10 21 kg as Fe, totaling 3-5×10 21 kg or a few percent of Theia's core. This mass is comparable to the excess Fe of 2.3-10×10 21 kg in the Earth's mantle inferred from the veneer component. Chemically in this hypothesis, Fe metal from Theia's core entered the Moon-forming disk. H 2 O and Fe 2 O 3 in the disk oxidized part of the Fe, leaving the lunar mantle near a Fe-FeO buffer. The remaining iron metal condensed, gathered Pt-group elements eventually into the lunar core. The silicate Moon is strongly depleted in Pt-group elements. In contrast, the Earth's mantle contained excess oxidants, H 2 O and Fe 2 O 3 , which quantitatively oxidized the admixed Fe from Theia's

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The tethered Moon

Cited by 58 publications

References 48 publications

Geological and Geochemical Constraints on the Origin and Evolution of Life

Geological and Geochemical Constraints on the Origin and Evolution of Life

Collisionless encounters and the origin of the lunar inclination

Asteroid bombardment and the core of Theia as possible sources for the Earth's late veneer component

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